The (Al,Ga,In)N material system includes materials having the general formula AlxGayIn1-x-yN where 0≦x≦1 and 0≦y≦1. In this application, a member of the (Al,Ga,In)N material system that has non-zero mole fractions of aluminium, gallium and indium will be referred to as AlGaIN, a member that has a zero aluminium mole fraction but that has non-zero mole fractions of gallium and indium will be referred to as InGaN, a member that has a zero indium mole fraction but that has non-zero mole fractions of gallium and aluminium will be referred to as AlGaN, and so on. There is currently considerable interest in fabricating semiconductor light-emitting devices in the (Al,Ga,In)N material system since devices fabricated in this system can emit light in the blue wavelength range of the spectrum. Semiconductor light-emitting devices fabricated in the (Al,Ga,In)N material system are described in, for example, U.S. Pat. No. 5,777,350.
FIG. 1 is a schematic view of a typical semiconductor laser device (or laser diode—“LD”) 10 fabricated in the (Al,Ga,In)N material system. The device is able to emit light in the blue wavelength range.
The laser device 10 of FIG. 1 is grown over a substrate 1. In the laser diode 10 of FIG. 1 the substrate 1 is a sapphire substrate. A buffer layer 2, a first cladding layer 3 and a first optical guiding layer 4 are grown, in this order, over the substrate 1. In the embodiment of FIG. 1 the buffer layer 2 is a n-type GaN layer, the first cladding layer 3 is an n-type AlGaN layer, and the first optical guiding layer 4 is an n-type GaN layer.
An active region 5 is grown over the first optical guiding layer 4.
A second optical guiding layer 7, a second cladding layer 8 and a cap layer 9 are grown, in this order, over the active region 5. The second optical guiding layer 7 and second cladding layer 8 are of opposite conductivity type to the first optical guiding layer 4 and first cladding layer 3; in the laser device 10 of FIG. 1 the first optical guiding layer 4 and first cladding layer 3 are n-type so the second optical guiding layer 7 and second cladding layer 8 are p-type layers. In the laser device of FIG. 1 the second optical guiding layer 7 is a p-type GaN layer, the second cladding layer 8 is a p-type AlGaN layer, and the cap layer 9 is a p-type GaN layer.
The structure of the active region 5 of the laser device 10 is not shown in detail in FIG. 1. In general, however, the active region 5 will be either a single quad well (SQW) active region having one quantum well layer disposed between first and second barrier layers, or a multiple quantum well (MQW) active region having two or more quantum well layers with each quantum well layer being disposed between two barrier layers. The quantum well layer(s) may be, for example, layers of InGaN, AlGaN or AlGaInN.